2006 Explorer Transmission Problems

[JRC Explorer]

I have a 2006 Explorer Eddie Bauer 4.6L V8. Started having problems with the transmission a few months ago. It initially began with a back and forth shifting feeling around 35MPH-50MPH at higher and lower speeds everything was pretty normal. Then one day it stuck in 2nd/3rd gear for a few minutes, after I stopped and started the engine it starting shifting again. After researching options for repair/replacement of transmission I decided to have it rebuilt. When I picked it up I thought my problems were over. The shifting was smooth and the issue with the back and forth shifting at mid-range speeds was gone. A few days later for just a few minutes it stuck in 2nd/3rd gear again then started working normally. I took it back to the shop and they drove it around for 1 1/2 days and could not duplicate the problem. I picked it up and drove it for several days without any problems again. Then it stuck in lower gear again I was able to force a shift by manually shifting the gears and letting off the gas, etc. Now I am being told the valve body needs replaced? Before I do anything else can anyone point me in the right direction or make suggestions on how to proceed?